This invention relates to a methods and systems for controlling the distribution of high pressure petroleum well treatment fluids from a single supply conduit for injection into multiple petroleum wells at individually adjustable rates. More specifically, the present invention relates to a system and method for controlling injection rates which avoids small orifices which may block the injected chemical.
The efficient production of oil and gas from subsea wells requires the injection of various treatment chemicals to solve production problems such as corrosion, scale, paraffin, emulsion, and hydrates. Most current chemical injection systems for petroleum wells have a separate chemical supply conduit for each chemical and each well. Often several wells are located near each other, but at significant distance from a surface location for chemical pumping. Prior art systems have been proposed to remotely control the distribution of chemicals to each well at each well""s required rate while supplying a field of wells with a single conduit per chemical, as evidenced by the Skoflow system marketed by Flow Control Industries, Inc.
Producing fields with multiple wells, commonly offset at distances of more than 10 miles from the wells to a pump station, and multiple wells located in water depths of more than 900 feet, need a reliable method to control and monitor the distribution of chemicals from a common supply conduit to each well. Prior art equipment has been based on a pressure compensated flow control device which uses a pressure regulating valve in combination with an orifice to regulate the chemical flow at each well. An alternative system with an electric motor driver for a tapered variable clearance screw-shaped passageway is promoted by Scanna. Control is provided by remotely adjusting the orifice size or the pressure regulator valve setting which controls the differential pressure across the orifice. Some devices utilize a fixed large orifice and an adjustable orifice.
A major disadvantage of prior art methods of control and related systems is the small orifice size required to provide a low flow rate; some chemicals require only one or two gallons per day while the common supply conduit must be pressurized to a level to cause flow into the highest pressure well in the field. A differential pressure of several thousand pounds per square inch must flow through a very small orifice to provide flows of a few gallons per day. Contamination by small particles is likely in a sub-sea conduit of many miles length, and these particles can clog the small orifice of prior art systems. Repair or replacement of the plugged orifice may cost hundreds of thousands of dollars.
A separate feedback device is commonly used to determine the actual rate of chemical flow into each well in order to verify adjustments and provide confidence of well treatment. Accurate measurement of low flow rates at high pressure in a sub-sea environment is very expensive.
The disadvantages of the prior art are overcome by the present invention, and an improved method and system for controlling the distribution of well treatment fluids from a single supply conduit for injection into multiple petroleum wells at individually adjustable rates is hereafter disclosed.
A chemical injection control system constructed in accordance with the present invention includes a remotely operated two position directional control valve fluidly connected to a supply conduit, and a hollow cylinder having a cylinder bore and a first input-output port at one end of the bore. A barrier, such as a piston, separates variable sized chambers between the first and the opposing second input-output port. The second input-output port is fluidly connected to the directional control valve, such that high pressure fluid flows from the supply conduit through the control valve, through one side of the cylinder and forces the piston to displace a fixed volume of fluid from the cylinder bore and through the control valve, then from the discharge port of the control valve to an injection point for an individual petroleum well. Each operation of the directional control valve reverses the travel of the piston in the cylinder bore and causes another fixed volume of fluid to be injected into the individual petroleum well.
A two-position four way directional control valve may be remotely operated by an electric signal or a hydraulic signal, and is of a commercially available design that may accommodate the pressure and flow rate of the injected chemical with great reliability.
It is a feature of the invention that a pressure transducer may be connected to the discharge port of the control valve so that observation of the pressure drop at the valve discharge port may be used to determine the end of travel of the piston or other barrier within the cylinder bore, and thus detect or mark the fixed volume of chemical injected into the injection point of the well. This provides an inexpensive, reliable, and accurate feedback of the actual rate of chemical flow into each well. A flow indication switch alternatively may be used to verify the completion of an injection stroke. A piston position switch alternatively may be used to verify the completion of an injection stroke.
It is another feature of the invention that timing of the actuation of the control valve determines the average chemical flow rate, and verification by a transducer confirms the delivery, i.e., xe2x80x9cxxe2x80x9d many gallons was injected within xe2x80x9cyxe2x80x9d seconds, the time between the actuation of an injection stroke and confirmation that the stroke is completed. No small orifices or contamination sensitive components is required.
In one embodiment, two pistons may be employed within the cylinder, with a hydraulic dampening chamber on one side of each piston filled with a clean fluid connected to a pressure compensated flow control valve, which may be adjusted to provide a near continuous chemical flow and avoid interruptions of flow while waiting for the proper time to pass after injection of a fixed volume of chemical is confirmed. This pressure compensated flow control valve may employ a small orifice, but the clean fluid used for dampening would not pose a risk of clogging this orifice.
The present invention has as its principal object a chemical injection system with a large flow path for the chemical so that flow blockage of an orifice by contamination of matter within the injected chemical is avoided.
Another feature of this invention is to provide a reliable, accurate feedback of chemical flow to verify operation and desired well treatment. The system according to the present invention may use individual components which are well known in the oilfield industry for their high reliability.
A preferred embodiment of the invention includes the feature of first and second pistons or other barriers moveable together within the cylinder, with a pair of dampening chambers in fluid communication with a remotely operated control valve.
It is also a feature of this invention to provide a simple control system so that conventional sub-sea control and communication systems may easily interface with this system.
A further feature of the invention is that a piston when used as the barrier may provide a valve on each end for engagement with a seat surrounding one of the inlet/outlet ports.
These and further objects, features and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings.